Embodiments of the invention relate to medical/surgical devices, systems and methods. More specifically, embodiments of the invention relate to devices, systems and methods for enhancing a knee surgery procedure.
Approximately 550,000 total knee replacement surgeries (also referred to as total knee arthroplasty (“TKA”) are performed annually in the U.S. for the treatment of chronic knee pain and dysfunction. As the U.S. and world populations become older and more obese, knee replacement surgery will become even more common, as knee joints endure greater and greater wear and tear from their increased loads and years of stress. Conventional TKA surgery is often very effective but also very invasive and sometimes imprecise, thus leading to less than ideal outcomes.
The knee is generally defined as the point of articulation of the femur with the tibia. Structures that make up the knee include the distal femur, the proximal tibia, the patella, and the soft tissues within and surrounding the knee joint. Four ligaments are especially important in the functioning of the knee—the anterior cruciate ligament, the posterior cruciate ligament, the medial collateral ligament, and the lateral collateral ligament. In an arthritic knee, protective cartilage at the point of articulation of the femur with the tibia has been worn away to allow the femur to directly contact the tibia. This bone-on-bone contact causes significant pain and discomfort. The primary goals of a TKA procedure are to replace the distal end of the femur, the proximal end of the tibia, and often the inner surface of the patella with prosthetic parts to avoid bone-on-bone contact and provide smooth, well-aligned surfaces for joint movement, while also creating a stable knee joint that moves through a wide range of motion.
In a TKA surgery, the surgeon cuts open the knee, flips the patella bone out of the way, cuts bone from the distal end of the femur and from the proximal end of the tibia, and installs new, manmade, prosthetic ends onto the femur and tibia to form a new knee joint. In some TKA procedures, the interior surface of the patella may also be covered with a prosthetic. Cutting open the knee, moving the patella, sawing off bone segments, and implanting the manmade implants is a very invasive, though effective, procedure. Determining how to cut the ends of the femur and tibia to ensure proper alignment and balancing of ligament tension in the new, prosthetic knee joint can be very challenging and often involves more art than science. An artificial knee joint in which the ligament tension is not well balanced endures significantly more wear and tear than one that is properly balanced, and yet, this proper balance is very difficult to achieve. As a consequence, TKA surgery performed on younger patients typically needs to be redone one or more times during the patient's life.
Due to the invasiveness and imprecision of traditional TKA, there is a need for improved techniques and devices in this field. A number of minimally invasive (or “less invasive”) TKA techniques, involving smaller incision sizes and reduced trauma to the patient have been developed in an effort to reduce patient recovery time. Some of these minimally invasive techniques, as well as other innovations, have also sought to enhance and/or facilitate TKA by making it more precise and repeatable and thus, ideally, reducing wear and tear on artificial knees and the need for repeat procedures. Improved techniques and devices would also mean enhanced outcomes for all TKA patients, with better functioning of the knee joint and longer useful life of the artificial knee.
One of the greatest challenges in TKA surgery is to properly balance ligament tension, especially in the medial and lateral collateral ligaments, through a full range of motion of the knee. The collateral ligaments, which connect the distal femur and proximal tibia on the medial and lateral aspects of the knee, account for much of the stability and movement of the knee. If one of the collateral ligaments is too lax or too tight relative to the other collateral ligament, the knee will typically be unstable, range of motion may be limited, the patella may move (or “track”) improperly, and the femur and/or tibia may wear unevenly, leading to arthritis and pain. Uneven ligament tension after TKA surgery will typically cause joint instability and poor patellar tracking, limited range of motion, and impaired function of the knee, as well as uneven, increased wear of the prosthetic device, which often necessitates repeat surgery. Thus, it is imperative for the short- and long-term success of a TKA procedure to achieve balanced ligament tension in the knee through a full range of motion.
Balancing ligament tension during TKA surgery is complicated by the fact that the natural knee does not operate like a hinge moving about a single axis. The knee exhibits dynamic external rotation of the tibia relative to the femur as the knee moves from its flexed to its fully extended position. This automatic rotation of the tibia occurs in the opposite direction when the knee is flexed from its fully extended position to produce an internal rotation of the tibia relative to the femur. Thus, the natural knee exhibits a rotary laxity that allows the tibia to rotate through a limited internal and external arc during knee flexion. In addition, the femur translates anteriorly and posteriorly as the tibia is being flexed about it, bringing yet another movement variable into the equation. Thus, the ligaments of the knee, along with the femur, tibia and patella, create a truly dynamic bio-mechanism, making ligament tension balancing in TKA surgery extremely challenging. This challenge is even greater in minimally invasive TKA procedures, in which incisions are smaller than those made in “open” TKA surgeries. Additionally, the incision made during minimally invasive TKA surgery is biased to the medial side, leaving the lateral side of specifically the distal femur “closed” to access of front or end loaded surgical instruments
One way surgeons try to balance ligament tension during TKA procedures is by cutting one or more ligaments to release tension from one part of the joint (“ligament release”). The disadvantage of ligament release, however, is that once a ligament is cut it cannot be regenerated, and the ligaments of the knee provide much needed stability to the knee joint.
Rather than or in addition to ligament release, the components of a total knee prosthesis may be selected and positioned to balance ligament tension. Since the femoral and tibial components of the knee prosthesis are attached to cut surfaces of the distal femur and proximal tibia respectively, placement and orientation of the femoral and tibial bone cuts are very important for balancing knee ligament tension. As with ligament release however, it is often very challenging to position the femoral and tibial bone cuts and prosthetic components to provide ideal ligament tension through the range of motion. This is due primarily to the complexity of motion about the knee, as described above, and the difficulty of assessing and making the bone cuts during the procedure to achieve desired ligament tension through the full range of motion.
Improved methods and apparatus for facilitating and/or enhancing femoral bone cuts have been described in, for example, U.S. Pat. Nos. 7,578,821 and 7,442,196. The assignee of the present application has also described various embodiments of a method and system for facilitating and/or improving tibial bone cuts in a TKA procedure in U.S. patent application Ser. No. 12/729,222, filed on Mar. 22, 2010, the full disclosure of which is incorporated herein by reference.
To make a tibial cut in a TKA procedure, an orthopedic surgeon typically uses a cutting block or cutting guide temporarily attached to the front of the tibia via a rod that is typically attached to an ankle clamp at the distal end to the tibia (an extramedulary rod) and aligned approximately with the mechanical axis of the anterior surface of the tibia. The cutting block is used to guide a surgical saw blade or rotary tool in making the tibial bone cut. Positioning such a cutting block, therefore, is crucial to forming well-positioned bone cuts for attachment of the tibial and femoral prosthetic components. The tibial cut is the foundation of a TKA, as it affects the spacing, alignment and balance between the tibia and femur when the knee is in flexion (the flexion gap), the spacing, alignment and balance between the tibia and femur when the knee is in extension (the extension gap), and all points of articulation between extension and flexion. Typically, the tibial component of a knee prosthesis is positioned on a flat, horizontal cut surface of the proximal tibia (at a 90 degree “varus/valgus” angle relative to the long axis of the tibia), and the position and orientation of the tibial component typically do not vary greatly from knee to knee. By making a cut on the tibia at 90 degrees to the long axis of the bone, however, a bigger space is created laterally than medially, due to the tibia's natural approximately 3 degrees of varus slope. Furthermore, the “classic” 90-degree tibial bone cut is typically made by the surgeon simply approximating the 90-degree angle. Therefore, the usual cut made to the tibia in TKA is not necessarily ideal and is made by approximation. Thus, improvements to the angle and precision of the tibial cut may improve the ligament balancing and overall result of a TKA procedure.
Therefore, a need exists for improved devices, systems and methods for enhancing TKA surgery and specifically for enhancing and/or facilitating the positioning of one or more tibial bone cuts made during a TKA procedure to accommodate a tibial prosthetic. Ideally, such devices, systems and methods would allow a physician to effectively select an angle at which to make a tibial bone cut and would help the physician more accurately make the cut at the selected angle. Such devices, systems and methods would also ideally be simple to use in conjunction with cutting guides, saw blades or burs, robotic and navigational systems, and/or any other equipment used by a surgeon in a TKA procedure. At least some of these objectives will be met by various embodiments of present invention.